Battery always drains out

[rupert e.]

Hey guys anybody know what might be wrong with my 89 525i, this is the problem: the battery drains out whenever i dont use the car for a day or two. checked the alternator and the battery it seems to be ok, i got a new battery and after a few weeks it drained out as well any ideas? tnx

[KC Ron Carter]

you need an AMP meter to test with to find a power leakage issue.

My guess is the alternator is not putting out enough to keep the battery charged.

Alternator Regulator

They can wear into a grooved pattern and the impact of driving can make them vibrate out of the normal groove.

Since the regulator has to increase output to jump the gap it does.

You can clean up the slider rings with abrasive paper.

You can get the brushes as a separate part requiring soldering skills or you can get a Regulator brush assembly for $70.

I would recommend only Bosch, the others are always suspect.

Some instruction for changing:

It is a very touchy installation and about 5% of the installation end in the ground link bent and the alternator not functional.

You can remove correct and reinstall the regulator.

The output must be 14.25 or higher on a Volt Ohm Meter not the dash gauge.

Some hints on the regulator change.

Replacing Alternator Regulator

For those who work on their cars and have not had alternator problems, here is a simple action that should save you down-time and significant costs.

Most alternators on German cars fail due to brushes wearing down (as they are supposed to) between 150k and 200K miles. Brush replacement is very easy -- it should not take over 20 min. and the brushes are attached to a new regulator.

To replace regulator assembly -- back of alternator held in place with two straight slot headed screws. This has a round transistor mounted on the outside on Bosch alternators -- the other type is similar but uses different brushes. Pop the regulator out, after removing the screws.

Fitting the regulator back is simple, but you must install it starting at an angle, to assure that the brushes compress when the regulator is flush with the alternator and the screws are tightened.
You are now ready for 200K miles of alternator life.



Later,

[Filehorse 525i]

B4 you start replacing electrical components, you need to check and be sure you don't have a partial short to ground (load) when the vehicle is off. To check this, you'll need a DC ammeter. With everything turned off, there should be no more than a few milliamps (maybe a hundred milliamps or so) drain to keep the clock ticking and a few other electronic components (remote entry, intrusion alarm, etc.) awake and listening. If you have upwards of 1 amp or more current flow with everything off, you have a partial short somewhere which is probably in the form of a failed relay or circuit board component that replacing/rebuilding the alternator will not help. Hopefully, it is the charging system and that will be easier to fix than chasing down the source of a mystery current drain. A service manual should tell you what the baseline current flow should be.

Lotsa luck.